The present invention relates to a crank arm for bicycles and the crank includes two ends with a hollow aluminum tube connected therebetween. An outer layer made of compound material is coated on the tube and the two ends.
A modern idea for making a crank arm for bicycles is focused on less weight and high strength. One of the conventional methods for making the crank arm is to make two ends and a hollow tube in separate, each of the two ends has a connection portion which is inserted in the hollow tube and the two connection portions are connected with each other in the hollow tube. The hollow tube is filled with the two connection portions and the weight is still not satisfied. Another conventional crank arm is made from a one-piece metal which is rolled to have the desired shape and structure. It is found that there are two narrow neck portions located close to the two ends and the structural strength and the two narrow necks tend to be broken when suffered by stress.
The present invention intends to provide a crank arm that has a hollow tube and two ends which are connected to the two ends of the tube. A compound material layer is coated to the crank arm to reinforce the structural strength of the crank arm.
In accordance with one aspect of the present invention, there is provided a crank arm for bicycles, wherein the crank arm comprises a hollow tube with a first end piece and a second end piece connected to two ends of the hollow tube. The first end piece has a first engaging hole defined therethrough and the second end piece has a second engaging hole defined therethrough. Each of the first end piece and the second end piece each have an insertion for being inserted in two ends of the hollow tube. A compound material layer is coated to the outside of the hollow tube, the first end piece and the second end piece.
The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention.